1. Technical Field
This invention relates to weight lifting equipment. More particularly, it pertains to a method and apparatus for continuously varying the resistance force exerted by the lifting bar of a weight lifting device.
2. Description of the Prior Art
Generally speaking, there are two types of weight lifting devices in common use today. Each has its own advantages and disadvantages.
One such type is the free-weight barbell. The typical barbell uses a lifting bar with one or more weight plates attached near each end of the bar. The weighted bar is grasped by one or two hands and raised and lowered through an exercise cycle. Some barbells, typically those with a shorter bar, are intended for use primarily for one-handed exercises. These shorter barbells, known as dumbbells, can employ a one-piece construction which combines the lifting bar and weight plates into one piece which prevents varying the fixed weight of the barbell for different exercises for different users. Other barbells, typically those with a longer bar, are intended for use primarily for two-hand exercises. These longer barbells typically employ removable weight plates of various individual weights and means for adding and removing the individual weight plates to and from each end of the bar to vary the fixed weight of the barbell for different exercises and for different users.
The second common type of weight lifting device is the selectorized weight lifting machine which employs a stack of weights channeled for being raised and lowered by a cable and pulleys which connect the stacked weights to a lifting bar. As the lifting bar is raised and lowered through an exercise cycle, a number of the stacked weights, pre-selected by the user for the particular exercise, are raised and lowered. The stacked weights, cable, pulleys and lifting bar are generally interconnected structurally and the path of the lifting bar is typically predefined by the structural connections, unlike the lifting bar of the typical free-weight device which can be moved freely without restriction.
The resistance force of a lifting bar of the more common types of weight lifting devices, against which a user raises and lowers the lifting bar, is fixed and constant through an entire exercise cycle. While benefits of weight lifting with such a fixed and constant resistance force have been well known for many years, the added benefits of weight lifting with a variable resistance force, one which increases as the amount of force required of the body through an exercise cycle decreases and which decreases as the amount of force required of the body through an exercise cycle increases, have become well known more recently.
For weight lifting, power is determined by the amount of force required of a body to move a lifting bar over a prescribed distance in a resultant amount of time. While the time and distance components for determining power remain fairly constant for most exercises, the amount of force required of a body through an exercise cycle will typically vary due to the musculoskeletal features of the body. As a user approaches the midpoint of an exercise cycle, there is typically less difficulty in raising or lowering a lifting bar (i.e. less force required). Conversely, as a user returns to the start and end point of an exercise cycle, there is typically more difficulty (i.e. more force required). Power or strength training to compensate for natural musculoskeletal variations in the amount of required force, with time and distance remaining fixed, involves increasing the resistance force of the lifting bar as the required lifting force decreases in an exercise cycle and decreasing the resistance force of the lifting bar as the required lifting force increases. Power training can permit a user to realize more significant gains in a person's strength and muscle development in a shorter period of time as compared to weight training with a fixed and constant resistance force.
U.S. Pat. No. 5,029,849 discloses an apparatus for varying the resistance force through a defined portion of an exercise cycle. It uses a rather complex series of cords, clips, straps and buckles, in addition to a mechanical type of variable resistance means. The device is intended to apply a variable resistance force through the second step of a defined three-step process of raising and lower a lifting bar. It further discloses means for loosely connecting the apparatus to an end of a lifting bar outside of the weight plates or, presumably, inside the weight plates, assuming the weight plates are removable and the user is inclined to first remove both the weight plates and the means for retaining the weight plates on the lifting bar. This invention further discloses means necessary for physically adjusting the length of the device for physical size differences between individual users.
It is an object of the present invention to provide a variable resistance force to a lifting bar of a weight lifting device throughout a complete exercise cycle. It is a further object of the present invention to provide an apparatus which permits a safe, quick, and easy connection to and removal from the lifting bar of such a device without the need to remove any weight plates. It is a further object of the present invention to provide a device which minimizes the need to adjust the length of the apparatus for physical size differences between individual users. It is yet a further object of the present invention to provide means for allowing a particular user to easily increase the amount of variable resistance force to use for a particular exercise.